You could upload a file on the hosting server using the following C# code:

C# 8.0 and .NET Core 3.0 – Modern Cross-Platform Development: Build applications with C#, .NET Core, Entity Framework Core, ASP.NET Core, and ML.NET using Visual Studio Code, 4th Edition
ASP.NET Core 3 and Angular 9: Full stack web development with .NET Core 3.1 and Angular 9, 3rd Edition
C# in Depth, 4th Edition

String sPath = Server.MapPath(“UploadFolder”);

String sFileName = “YourFileName.txt”

File.SaveAs(sPath + sFilename);

Right-click on the folder (UploadFolder folder), and then select Properties. In the Properties dialog box, click on the Security tab and make sure the ASP.NET Machine Account is included in the list and has the proper permissions to write to disk